1. Field of Art
The present invention generally relates to the field of digital video, and more specifically, to methods of quantifying the value of high-quality video transcoding.
2. Background of the Invention
Video codecs, such as MPEG-4 Part 2, MPEG-4 AVC, H.261, H.263, WMV, DIVX, and the like encode a video from an uncompressed source format to compressed format. Video codecs can be either lossless or lossy. A lossy codec may reduce the subjective or perceptual quality of the video relative to the original source video, leading users to have a less positive viewing experience. Thus, for some videos it can be beneficial to use a higher-quality video codec, or a higher-quality setting for a given video codec, that may result in less compression but higher-quality video output to improve the perceived quality of the video. For other videos, however, use of a higher-quality video codec does not produce perceptibly superior results to a human viewer, and thus the amount of added data required to represent the video is not justified.
Video hosting services, such as YOUTUBE or GOOGLE VIDEO, allow users to post videos. Most video hosting services transcode an original source video from its native encoded format (e.g., MOV) into a commonly available format (e.g., ADOBE FLASH or Windows Media Video (WMV)) at a lower quality. The transcoding comprises decoding the source video from the native format into an unencoded representation using a codec for the native format and then encoding the unencoded representation with a codec for the commonly available format. This reduces storage requirements, and also reduces the bandwidth requirements for serving the video to clients. As memory costs decline and high speed connections become more prevalent, it has become possible to store and provide high quality versions of source videos. However, merely storing a high quality version of every video is inefficient, since, as noted, a high quality encoding of a video is not necessarily perceptibly visually superior to a lower quality encoding of the same video. Thus, it is useful to define and apply selection criteria to determine whether or not to create and store a high quality transcoded version of a given video, rather than, or in addition to, a lower quality version.
Existing selection criteria analyze inherent, static characteristics of a given source video—such as its bitrate, dimensions, and the like—to determine whether or not the video is a good candidate for encoding via a higher quality algorithm. However, the use of such criteria sometimes produces poor results, leading to the performance of higher-quality encoding for videos that gain little, if any, additional visual quality by it, or failing to do so for videos that would benefit significantly.